# College Physics

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A radio station with a power of 20 kW sends out an omnidirectional wave at 1.25 MHz.

a. If the electromagnetic wave has an electric field of 0.22 V/m, what is the magnetic field amplitude?

b. What is the intensity of the wave at 5 km?

c. What is the wavelength of the electromagnetic wave?

• College Physics -

after 50 years in radio, I have no idea what an omni-directional antenna is. Does it radiate upwards? Downward? in a Donut shape? It is easier to just say the gain in db in a particular direction, and stop the nonsense about omnidirectional antennas. This is a real world.

c) frequency*wovelength=speedofLight
solve for wavelength.

This is what is normally called omni-directional antenna patterns by radio users, it is not OMNI in the sense physicists mean, a spherical pattern. http://www.inl.gov/featurestories/i/antenna_02.jpg

In this pattern, one has to know the flatness in azimuth, which is complicated. It is just much easier to specify gain in db over a the mythical spherical omni, which does not exist.

• College Physics -

That idea of "omni directional" kind of confused me also... I would guess that it can be assumed as just a regular wave?

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